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LIBRARY OF CONGRESS. 

Shelf ..y.\/„5 X 



UNITED STATES OF AMERICA. 



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The " Home College Series " will contain one hundred short papers on 
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New York, Jan., 1883. 






Copyright, 1868, by Phillips & Hunt, New York. 



iomt CoIIcgt gtrits. ftumbtr Sfbmtg-sttr^n. 
COMETS. 



The mysterious bodies called comets possess attractions 
that invest the study of astronomy with increasing interest. 
These bodies, from heights immeasurable, or from depths 
unfathomable, rush into view with a velocity of speed so 
great as, in many instances, to baffle calculation ; and then 
dash away again at nearly the same rate of speed, to thus 
traverse the regions of space through thousands of years. 
Comets owe their existence, motion, and continuance to the 
same causes, and are subject to the same general laws as the 
planets. Unlike the planets, however, they are bodies of 
extreme lightness, small attractive power, little disturbing 
influence; and of such strange behavior as to almost defy 
calculation. 

I. General View of Comets. 

The movements of these fiery-visaged strangers are the 
subject of great interest and close study. They have orbital 
motions, ranging from less than that of the earth The motion of 
to more than fifty times as great as Neptune. The comets, 
rate of motion varies greatly at different points in the orbit 
of a comet. Nearest the sun it reaches the highest rate of 
speed. At one period it comes so near that body that it 
seems about rushing into it; at another time it is so remote 
it would seem to be forever beyond the reach of its attractive 
power, and could never be brought back to feel its scorching 
heat. The extreme point in the orbit of the comet of 1680 
is estimated to be twenty-eight times the distance of Neptune, 
the outermost planet of our solar system, or seventy thousand 
millions of miles distant from the sun. Without any warn- 
ing, this body of ghostly light came, suddenly sweeping 
down upon us from the heights above, almost in a perpen- 
dicular line to the sun; and, approaching within about one 



COMETS, 



hundred thousand miles of that body, swept around it with 
the startling velocity of ten hundred thousand miles an hour! 
The comet of 1843 attained the terrific speed of one million 
miles an hour as it wheeled around the sun. It approached 
so near as to almost graze the luminary of day. Its temper- 
ature was estimated to be forty-seven thousand times greater 
than the fiercest heat of the torrid zone ! The heat received 
from the sun by the comet of 1680 was estimated, from a 
careful calculation made by Sir Isaac Newton, to be two 
thousand times hotter than red-hot iron ! 

Just here the question arises, How can a body subjected to 
such excessive heat escape being entirely consumed ? That 
comets survive exposure to an enormously high temperature, 
approach so near with such great velocity, and yet do not 
plunge into the sun, adds no little to the difliculty of explain- 
ing their mysterious character. 

Peculiar form One rate of speed on the curve around the sun 
of orbits. indicates an oval-shaped orbit or path. Comets 
having this elliptical orbit return again and again, revolving 
around the sun in various periods of time, according to their 
distance from that body. Still greater velocity may indicate 
a parabolic (a wider) or a hyperbolic (a still wider) curve, 
precluding the possibility of return. Such comets evi- 
dently can only rush down upon us, or up to us, and dash 
rapidly around the sun, and then off into infinite space, never 
to return. Therefore certain comets are but transient visit- 
ors, many of which necessarily come and go without recog- 
wh are no ^^^^^^ ^7 ^S' "^^ attraction of planets may either 
more comets SO accelerate or so retard the speed of a comet as 
^^^'^ • to change its orbit from elliptical to parabolic, or 

from parabolic to elliptical. But in any case only a very 
small part of its orbit can be studied by us, since the comet 
can be seen only when near the sun. Many, by reason of 
their dimness and small size, must entirely escape our notice. 
No doubt the greater number of these bodies are invisible to 



COMETS. 3 



us because they come and go during the day and moonlight 
nights. Because so rarely seen, the general supposition is 
that there are but few comets in existence. The immense num- 
contrary is true. Like that of meteors, the num- ^^^ ^^ comets. 
ber is exceedingly large. No doubt they are the most nu- 
merous *of all the heavenly bodies. During the Christian era 
upward of five hundred have been seen by the unaided eye. 
The telescope from the time of its invention has revealed 
two hundred more. Taking these figures, and making due 
allowance for those escaping our notice, those belonging to 
our solar system must, unquestionably, be numbered by 
millions. Arago, the eminent astronomer of France, places 
the number at more than seventeen millions. Lambert, of 
the same country, says they can number no less than five 
hundred millions. Prof. Peirce says more than five thousand 
millions 

II. The Tkaii^" of Comets. 

By far the larger number of comets have no trains, and 
are too faintly luminous to be often seen without a telescope. 
These are divided into two classes : those without a nucleus, 
but of uniform density throughout their whole mass; and 
those having a nucleus or head, which is the brightest and 
most condensed part of the comet. Comets of this latter 
class are often of vast magnitude, but of extreme lightness, 
and having but a small quantity of matter, as compared with 
their bulk. Comets having a train accompanying the main 
body constitute a third class. It is only the members of this 
latter class that are generally seen by the unaided eye. The 
hair-like appeai*ance of the train procured for these bodies 
the name " comet," from the Greek word " coma," meaning 
hair. These trains are really most wonderful. The closest 
and most careful investigations with our improved astronom- 
ical instruments, while definitely settling some points, have, 
in the main, deepened our desire to know, and yet fallen 
short of perfectly satisfactory results. However, with the 



COMETS. 



data at hand, an interesting and far from profitless study- 
may be made of their composition, rapidity of formation, 
Number of length, and number, or divisions. The train of a 
trains. comet does not always remain single, but fre- 

quently separates into two, three, or more tails. The comet of 
1744 had its fan-shaped train separating into six streamers. 
Its edges were very bright, while the middle was of fainter 
light. Altogether it presented a most beautiful and mag- 
nificent appearance. The one which so terrified Pope Calix- 
tus in 1456 had a train curved like a cimeter, or rather like 
the graceful form of an ostrich feather. It was this pope 
who gave to the Roman Catholic Church the prayer, " Lord, 
save us from the devil, the Turk, and the comet." A great 
victory was claimed for the powerful pope, when the comet, 
which had been duly anathematized and excommunicated, 
began to recede, and soon disappeared. 

In 1825 a comet appeared "which was visible for the unusual 
period of one year. Its time of revolution is supposed to be 
not less than four thousand years. Its train separated into 
five distinct parts, spreading out to an immense distance, and 
covering a large part of the heavens. The colors of these 
parts were variable, producing the most striking effects. 
Length of Pcrhaps the most marvelous feature of these 
trains, strange bodies is the fact of cometary matter 

streaming out to such enormous lengths, and yet remaining 
in actual connection with the comet. Their measurement is 
no mere matter of conjecture. Because of their size and 
distinctness, a good degree of accuracy may be realized. A 
most brilliant comet appeared in 1769, which passed within 
two millions of miles of the earth. This beautiful comet, 
moving with immense swiftness, was seen in London; its tail 
stretched across the heavens, like a prodigious, luminous 
arch, thirty-six millions of miles in length. The computed 
size of that which appeared in 1811, and which was so re- 
markably conspicuous, was, on October 15, according to 



COMETS. 



Dr. Herschel, fifteen millions of miles at its greatest breadth, 
and at the same time one hundred and thirty millions of 
miles in length. This comet far outrivaled the brilliant 
comet of 1858, (Donati's,) that was forty millions of miles in 
length ; and was surpassed in turn by the overwhelming 
splend6rs of the comet of 1843. "A fine drawing of this 
comet, as seen March 3, 1843, by C. Piazzi Smyth, Esq., at 
that time assistant astronomer at the Cape of Good Hope, 
now Astronomer Royal for Scotland, represents the train as 
highly symmetrical, giving the idea of a vivid cone of light, 
with a dark axis, and nearly rectilinear sides, inclosed in a 
cone somewhat fainter, the sides of which were bent slightly 
outward." The train of this amazing body streamed off to 
the distance of two hundred millions of miles. " It was of 
sufficient length to reach from the earth to the sun and back, 
again from the sun to the earth, and nearly twenty millions 
of miles over. It would have girdled the earth at the 
equator no less than eight thousand times." The great 
comet of 1861 was first seen by Mr. Tebbutt, at Sidney, in 
Australia, May 13; by M. Goldschmidt and others, in France 
and England, on June 29 and 30. The nucleus was about 
four hundred miles in diameter, with a long, bush-like tail, 
traveling at the rate of ten millions of miles in twenty-four 
hours. On June 30 it was suggested that we were in the 
tail, there being a phosphorescent, auroral glare. 

M. Babinet, on May 4, 1857, affirmed that comets had so 
little density that the earth might pass through the tail of 
one without our being aware of it. It is a wonderful fact 
that matter so thin, thinner by far than the thinnest mist, 
should be able to sustain any connection with the main body 
of the comet, as in the case of that of 1843, at the incredible 
distance of two hundred millions of miles. But the wonder 
increases as we learn the fact, that this same matter of ex- 
ceeding thinness keeps pace with the nucleus or head itself 
as it wheels with the frightful velocity of one million miles 



COMETS. 



an hour around the great solar orb, to sweep into the infinite 
heights above, or to plunge into the depths of space below. 
Eapidity of Another interesting feature of these trains is 
formation. ^qq^i in the rapidity of their formation. It re- 
quired but two days for the comet of 1680, which terrified 
the people with its near approach to the earth, to send out a 
train sixty millions of miles in length. In less than twenty 
days that of 1843 produced the enormous train of two hun- 
How and of dred millions of miles. As might be expected, 
what produced? ^he questions, of what material are these trains 
composed ? and how are they formed ? have excited great 
interest, and served to stimulate investigation. It is now 
generally conceded that the trains are of the same material 
as the nucleus or head of the comet. In reaching this result 
the larger telescopes have played a not unimportant part; 
but the most valuable service has been rendered by that 
modern wonder of constructive genius, the spectroscope. 
Through its aid these mysterious wanderers come to be 
known as largely gaseous bodies, having trains also of gase- 
ous matter, only less dense than the body of the comet. This 
much is certain ; but the nature of this matter or gas we 
cannot always determine. We have already referred to its 
extreme thinness. It is so transparent that through thousands 
of miles of cometary matter the faintest star may be seen. 
What can it be ? A very little of the cloudy vapor from 
water obscures the vision. Hydrogen gas is too heavy and 
dense, though it is sixteen times as light as air. We are 
certainly not familiar with all the conditions of matter, since 
none of those with which we are acquainted serve to explain 
fully the ethereal, and we might almost say spiritual, form 
it assumes in comets. It has been claimed that Prof. Peirce 
has demonstrated "that the nucleus of the comets of 1680, 
1843, and 1858 must have had a tenacity equal to steel to 
prevent being pulled apart by the tidal forces caused by its 
terrible sweej) around the sun." The head of the comet of 



COMETS. 



1843 was diminished by the manufacture of a train. In cer- 
tain instances an appreciable diminution in the size of trains 
has been discovered at successive returns. This indicates 
condensation or loss. The theory that these bodies, as the 
spectroscope indicates, are mainly gaseous, would permit 
cometary matter to be vaporized and driven off by the sun, 
as steam from a locomotive. But if wholly gaseous, would 
not comets be entirely dissipated when subjected to such in- 
tense heat from the sun, while under no form of compression 
other than its own ? Therefore, we hold comets to be com- 
posed of both gas and small masses of matter, more or less 
of a liquid condition, and affording sufficient attraction to 
maintain their unity, though suffering some loss by vapori- 
zation when nearest the sun, and by attraction when nearest 
the planetary bodies. A comet, first examined in 1818 by 
Encke, was identified by him with the one seen in 1805, 1795, 
and 1786. Its return has been observed ever since at periods 
of 3]^ years. This comet is celebrated for having revealed, 
as many astronomers think, the existence of a resisting me- 
dium in the interplanetary spaces. Herschel and others dis- 
sent from this view of Encke, and attribute the change in the 
comet's motion to the gradual loss of its tail. The motion 
of a comet's train is peculiar. The nucleus obeys the law 
of gravity, apparently uninfluenced by this peculiar motion. 
The material of the train first moves toward the sun, and is 
then repelled from it. This evident polarity leads to the 
natural conjecture that the train is due largely, if not entirely, 
to electricity. Electricity is venerated by heat : 

1 ;\ J 1 r ' .' mi -I Planetary bod- 

it IS also produced by iriction. ihe accumula- les affected by the 
tions of electric force on the sun must be incon- electricity of the 
ceivably great. It must be so, because of a ^^' 
temperature there so high as to be without a parallel. It 
eould not be otherwise, from the enormous friction of its 
ceaselessly raging elements on such a stupendous scale. This 
electricity, by a process called induction, passes to other 



COMETS. 



bodies more or less remote. The electric throbs of this great 
heart of the solar system are felt throughout all its parts. 
Our globe is no exception, and doubtless many of its phe- 
nomena may be traced to this source. 

In the absence of thunder-storms, and indeed of all ordi- 
nary electrical phenomena, electric currents have been known 
to sweep over the entire surface of the earth, and so as to 
seriously impede telegraphic operations. This is usually said 
to take place at the period of the greatest number of " sun 
spots,*' which is naturally supposed to be the period of the 
greatest activity of the solar forces. We find a probable ex- 
planation of the peculiar motion of trains in the powerful 
The electrical elcctrical influence which the sun exerts in a great 
influence of the degree upon the comets, no less than upon the 
sun on comets, pi^^gi^g^ jj^ l^j^jg explanation we are also largely 
helped toward the solution of other problems concerning 
comets. To possess the key to cometary mysteries we must 
understand somewhat of the sun's electrical influence over 
comets. To do this we must bear in mind the twofold prop- 
erty of electricity ; namely, its attractive and repelling force. 
Bodies charged with like electricities repel each other ; but 
when with unlike they will attract. The superior attractive 
power of gravitation resident in the sun draws the comet to 
him with ever-increasing velocity, until it is at perihelion — • 
nearest the sun — when, from some cause, it begins and con- 
tinues to recede with a velocity ever growing less and less. 
The comet's retreat is due to the repellant power of like 
electricities in the two bodies. The nearer the comet's ap- 
proach to the sun the greater the quantity of electricity, 
generated by the sun's heat, upon the surface of the comet. 
At perihelion the repellant force of these similarly charged 
bodies has reached such a degree, with the increase of elec- 
tricity on the comet, as to overcome, measurably, the power 
of gravitation, and the comet sweeps off again into space, 
never to return, unless the attractive power overcomes the 



COMETS. 9 



ever-waning repelling force. The comet's train is due to 
this electrical repulsion. The lighter portions of cometary 
matter are driven off by this repelling force in a continuous 
and ever-growing train as it nears the sun. When at peri- 
helion the train is fully developed, and remains so until, in 
receding from the solar center, it decreases as rapidly as it 
developed in its approach. Although trains have been seen 
at right angles to the line of motion, generally they are 
turned from the sun, whether the comet is approaching or 
retreating. This fact is an important one to the theory of 
electrical repulsion. The projections seen in some instances 
in front and at the sides of the comet, similar to the train 
itself, is probably produced by the electricity of the comet. 
This electricity, generated by the intense heat of the sun, 
throws off portions of the comet's more attenuated or thinnest 
matter, producing a hairy or brush-like appearance in the 
front of the body, and around the whole nucleus. The im- 
portant part played by electricity in cometary ^^^jtionai evi- 
phenomena is further established by the follow- dence of eiectric- 
ing considerations: The Aurora Borealis, or '^^ '° /^o^^^^s. 
Northern Lights, are confessedly occasioned by electricity. 
Though not so marked, yet very similar to the Boreal phe- 
nomena, are the tremulous vibrations of light, and slight 
changes of color, that may sometimes be seen throughout 
cometary trains. In addition to this, the magnetic needle 
was greatly agitated on the appearance of the famous comet 
of 1843. The property of the magnetic needle, causing it to 
point to the nx)rth, comes from the currents of electricity 
which girdle the globe from west to east. Any natural dis- 
turbance of this needle, coming from a source outside of the 
earth's surface or in the atmospheric regions, we may be sure 
is due to electricity. Therefore, the disturbance of this 
needle by the appearance of this comet and its enormous 
train favors the already well-supported theory, that elec- 
tricity was largely instrumental in developing this long 



10 COMETS. 



appendage; and, as a subtle, mysterious fluid, pervaded the 
whole wondrous length of that train. It afforded more than 
a show of reason for the supposition that this " same subtle 
fluid had power to leap in an instant, as it were, across the 
mighty chasm between the comet and the earth, and make 
itself seen and felt all over the surface of our own vast globe, 
and doubtless on every other globe belonging to our family 
of worlds. What a wonderful creature of the great Creator 
is this invisible fluid we call electricity ! " In the display of 
its amazing power we are led to marvel at the still more as- 
tounding power involved in its creation. It is folly to sup- 
pose it the mere product of chance. To say that it produced 
itself is to rave with hopeless madness. In the existence, 
wisdom, and power of God — the underived great First Cause 
— only can we account for this as well as other great and 
mysterious forces of both the universe of matter and the 
universe of mind. 

III. The Relations op Comets. 

Formerly comets were regarded as the forerunners of 

great events, and more particularly of great calam- 

is danger to be j^ies. The ignorant masscs, and even some of the 

apprehended .° J^ 

from comets? learned, as m the case of Fope Calixtns, were m 
a remarkable degree the victims of superstitious 
terror on the appearance of a comet. Even to this day they 
still produce intense excitement among savage tribes, being 
looked upon as precursors of famine, pestilence, and wasting 
war. " They sometimes call them * the spirits of the stars,' 
and employ various means to prevent the evil they are sup- 
posed always to bring — wildly and violently gesticulating 
toward the unwelcome visitor with fierce threats and fiercer 
expression of countenance, while they shoot arrows and dart 
javelins and hurl huge stones at the much-dreaded comet, 
Sloping to avert the threatened danger." 

Among more intelligent people of modern times supersti- 



COMETS. 11 



tious fear finds no place ; but the danger of a comet's col- 
lision with the earth has been seriously considered. In 1832 
some of the people of Paris were almost frantic with excite- 
ment in consequence of the prediction that the comet " Biela " 
of that date would come in contact with and destroy the earth. 
At the instance of the Government the French Academy 
of Science carefully estimated the chances of collision be- 
tween our globe and these apparently lawless wanderers. 
The report made by the great French astronomer Arago was 
that out of 281,000,000 of chances there was only one single 
chance for a collision. This amounts to but little more than 
a bare possibility. Should a collision take place, evil results 
might or might not follow. If the nucleus encountered was 
in mass and solidity equal to that of Donati's comet, as esti- 
mated by M. Faye and Prof. Peirce, " its impact with the 
earth would develop heat enough to melt and vaporize the 
hardest rocks." If the comet were composed of small mete- 
oric particles, the result would be a brilliant shower, exceed- 
ing such showers as we have seen only in degree. Were the 
colliding body a hydrogen comet of sufficient size to encom- 
pass the entire globe, it might so mingle with the oxygen of 
our atmosphere as to form such an explosive compound that 
the lighting of a single match would produce a mighty flame 
which, in an instant, would consume every living thing on the 
surface of the earth. Still further, since water is the result 
of burning hydrogen gas in oxygen, this same fierce and ter- 
rible flame would be as speedily followed by a mighty deluge 
of water, enveloping the entire surface of our planet. If the 
body of the comet were not of an inflammable nature, but 
composed of noxious gases, it would poison our atmosphere, 
render it unfit for respiration, and thereby entail the most 
serious consequences. Were it an innoxious gaseous body, 
owing to its extreme lightness it would float in or upon our 
atmosphere as do the clouds, without reaching the surface of 
our globe. 



13 C03IET8. 



It has been affirmed that the earth passed through the tail 
of the comet of 1861, a peculiar phosphorescent mist being 
Comet affect- *^® ^^^^ observablc effect. The comet of 1779 
ed by Jupiter's was diverted from its course by the four moons 
moons. ^£ Jupiter, and though carefully sought for it has 

never since that been seen. So little attracting power did 
this comet exert that the moons were not perceptibly effect- 
ed, and continue in their old paths. Hence it is possible the 
small quantity of matter contained in this comet was so pow- 
erfully attracted by these moons of Jupiter as to be drawn 
quite to, and become an atmosphere for, one or more of these 
globes. It is, at least, a plausible conjecture that 

conjee ure. ^^^ planet is indebted for its atmosphere to some 
comet or comets of the remote past. " It is possible that the 
air we now breathe, and which gently fans our fevered 
brows, comes to us laden with so many rich and delicate per- 
fumes from the flowers of spring, it is possible that this same 
air was once careering wildly through the vast abysses of 
space, a raging comet, attracting the wondering gaze of 
millions of inhabitants of other world." So far as we know, 
our world has not as yet suffered from these flaming sky- 
utiiityofcom- waudcrcrs. An almighty and beneficent Creator 
ets. upholdeth all things by the word of his power, 

and can, and no doubt does, compel these bodies of threaten- 
ing appearance to exercise a beneficial influence upon our 
planet. Certainly they serve a moral purpose by leading us 
to the contemplation of the boundless resources of our Crea- 
tor. Possibly they supply our atmosphere with some neces- 
sary gaseous elements, which are consumed or absorbed in 
the support of animal or vegetable life. In No. 42 of this 
Series mention is made of the intimate relation of meteors to 
comets — a relation the most intimate as to origin, flight 
through space, and service to other bodies. It is a supposi- 
tion, which has great show of reason, that comets and meteors 
probably furnish a portion of the fuel which aids in sustaining 



COMETS. 13 



the heat of the sun. Meteors, owing to the superior attrac- 
tion of the sun, doubtless fall more frequently into its atmos- 
phere than ijito that of the earth. The fact of the decrease 
of the periodic time of certain comets looks toward their 
ultimate absorption in the sun. After revolving around him 
for thousands of years, comets may at last be drawn to his 
surface by his superior attraction overcoming his repelling 
force. Modern discoveries tend to fix upon the origin of com- 
sun and the stars as the birthplaces for the comets. ®*3- 
The projectile or volcanic force of the sun, and that of a 
similar nature, though even greater in degree, upon the stars, 
sends matter out into space so far that it may never return, 
since it comes immediately under the influence of the sun's 
electric or repelling force. The theory of solar and of stellar 
expulsion and repulsion is the most plausible one for the origin 
of comets. 

Comets emit a great deal of light; but, after all. The light from 
they are not self-luminous. Like the moon and comets. 
the planets, they shine by the reflected light of the sun. As 
the comet changes its position around the sun, it exhibits 
phases similar to those of the moon as it revolves around the 
earth. If they shone by native light they would always ap- 
pear the same, as does the sun. But at one time the comet 
appears in the form of a crescent ; again as gibbous or bulg- 
ing; and yet again as round or full. In the development of 
these phases, however, comets differ from the moon. This 
difference is determined by the moon always moving in a 
fixed orbit, while comets move in all conceivable directions 
— "now coming from the east and going to the west ; from 
the north and going to the south ; from the south and going 
to the north; and then dashing down from the heights above, 
or rushing up from the depths beneath, and thus reaching 
the sun from all points of the compass." Some of cometic pe- 
the comets known to us are remarkable for the long "O'^s. 
intervals between their appearances. These long periods 



14 COMETS. 



from one visit to another are owing to the immense distances 
journeyed by them. This will be better understood if we 
recall to mind that the path or orbit traversed by a comet 
describes a very long oval-shaped figure. One end of this 
oval, in some instances, is only about one hundred thousand 
miles from the sun, while the other end is often many thou- 
sands of millions of miles distant in the opposite direction. 
Some comets visit us quite frequently. We have already 
spoken of the short period of Encke's comet. Biela's comet, 
which caused such fear in Paris, had a periodic time of six 
years and eight months. In January, 1846, it was observed 
to have separated into two parts of unequal brightness. 
When last seen in that year the parts were 200,000 miles 
asunder. At its next appearance they were 1,500,000 miles 
apart. It should have made three revolutions since that 
time, but no trace of it has been discovered since it vanished, 
in September, 1852. Donati's comet of 1858 is estimated to 
have a period of about 2,000 years. A period of 102,050 
years is attributed to the comet of 1844. The comet of 1744 
is said to have the longest period yet known to astronomers. 
It requires 122,683 years for this comet to make one revolu- 
tion around the sun. We have already noticed 

Cometic ex- ^ ^ "^ 

tremesofheat the intense heat to which comets are exposed 
and cold. when nearest the sun. Must they not experience 

a corresponding extreme of cold when receding so far from 
the sun into the depths of space? The lowest temperature 
of our Arctic regions must be mild in comparison. Is it not 
possible that these bodies — thinner than the thinnest vapor 
known to us — are greatly condensed by this intense cold, 
perhaps even to solidification ? Then, on again approaching 
the sun, they are once more converted into a gaseous condition. 
Ideas of space ^^ ^^^ helped to, at Icast, a faint conception of 
repulsion, and at" the immensity of space from the mighty wan- 
from'these wan- ^^^rings of comcts. ^ What unexplorcd regions 
derers of the skies of space must be visitcd by a comet, traveling 



COMETS. 15 



all the time in nearly one direction from the sun, for upward 
of 60,000 years ! How great must be the electric force of 
the sun to send this comet so far out into the dark abysses 
of space ! What wonderful power of attraction is exerted by 
the great luminary of day to arrest this fugitive in his farther 
flight ! This seemingly " lawless vagabond of the skies, ap- 
parently subject to no law, is, nevertheless, every moment 
of that flight feeling the strong grasp of its great Con- 
troller, standing majestically and blazing gloriously at the 
center of his great system, and at last this vagrant of the 
skies acknowledges his allegiance by turning back to its ma- 
terial lord, nor tarries in all the way until it has done its 
customary obeisance in his burning presence^" 



NOTES. 



" The laws of nature do not account for their own origin." 
— JoHx Stuart Mill. 

" It is certain that matter is somehow directed, controlled, 
and arranged, while no material forces or properties are 
known to be capable of discharging such functions." — 
Lionel Beale. 

" Science was Faith once ; Faith were science now, 

"Would she but lay her bow and arrows by, 

And arm her with the weapons of the time." — J. R. Lowell. 

" As we perceive the shadow to have moved along the dial, 
but did not perceive it moving; and it appears that the grass 
has grown, though nobody ever saw it grow; so the advances 
we make in knowledge, as they consist of such insensible 
steps, are only perceivable by the distance." 

"Ignorance is the curse of God, knowledge the wing 
wherewith we fly to heaven." — Shakesprare. 

" The whole earth is but a single mote in the star-dust 
with which God's creative hand has strewn the skies." 



16 COMETS. 



" Overhead the countless stars 

Like eyes of love were beaming, 
Underneath the weary earth 

All breathless lay a-dreaming." 

" The twilight hours like birds flew by, 

As lightly and as free ; 
Ten thousand stars were in the sky, 

Ten thousand in the sea; 
For every wave with dimpled cheek 

That leaped upon the air, 
Had caught a star in its embrace, 

And held it trembling there." 

"Flowers are stars wherein wondrous truths are made 
manifest.'* 

"Thoughts which fix themselves deep in the heart, as 
meteor stones in earth, dropped from some higher sphere." 



[THOTTGHT-OITTI-INE TO HELP THE MEMORY.] 

1. Laws by which Comets are governed? Motion of Comets? Peculiar form 

of orbits ? When Comets are seen ? Their number ? 

2. Nucleus? Train? Number of trains? Length of them? Illustrations? 

Theories about formation of trains ? Electrical effects ? Sun's influence ? 
Disturbances on our Earth? 
8. Danger? Arago's theory ? Jupiter's moons ? Atmospheric theory? Use 
of Comets ? Periodical appearance ? Extremes of heat and cold ? 



0:E3:.A.TJTJ5i.XJQXJ^ TEl^SiT-lBOOISlS, 



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